Flow sampling with top talkers

ABSTRACT

An improved network flow sampling apparatus and corresponding method more intelligently selects flows to be reported beyond random flow or packet sampling intervals. Evaluation of flows selects top talkers or heavy hitters as important flows that most impact traffic and therefore should be reported. Top talkers are flows defined based on a customized definition according to, for example, number of packets in a flow, number of bytes in a flow, or bandwidth consumed by a flow. An external collector can thus proceed with traffic profiling or other flow monitoring purposes with a more intelligently determined network flow sample.

BACKGROUND

1. Field

Embodiments of the invention relate to the field of flow monitoring; andmore specifically, to a more intelligent and dynamic sampling of networkflows.

2. Background

Network flows are monitored for a variety of purposes, includingusage-based accounting, traffic profiling, traffic engineering, attackor intrusion detection, and QoS (quality of service) monitoring. Onemethod of monitoring flows is performed by reporting on each and everyflow. While this implementation provides an accurate and completepicture of network traffic, it requires a large number of resources,including memory and CPU (central processing unit) usage on theforwarding plane of the network device, backplane bandwidth to send flowrecords to the control plane of the network device and also out to anexternal collector, memory and CPU usage on the control plane of thenetwork device, network bandwidth consumption due to heavy communicationwith the external collector, and memory and CPU usage on the externalcollector. Reporting on each and every flow is not feasible inhigh-speed environments.

An alternative to complete reporting of all flows is to report on asample of the flows. For example, sampling can be done in packetintervals. Packet interval sampling takes a random selection of a subsetof packets, e.g., by reporting on 1 out of every 1,000 packets receivedon a network device. However, there are various drawbacks of packetinterval sampling. One drawback is that this sampling does not provide aprecise number of packets in a flow. If the number of packets reportedis 1,000, one can only assume that there were approximately 1,000,000packets in the flow, but it is not an exact count. Another drawback isthat packet interval sampling tends to report longer flows rather thanshorter flows because if a flow contains fewer than 1,000 packets, asample may not necessarily be taken from this flow. For these reasons,packet interval sampling is not ideal.

An alternative to packet interval sampling is flow interval sampling.Flow interval sampling takes a random selection of a subset of flows,e.g., by reporting 1 out of every 5 flows, and reporting the selectedflows in their entirety. This sampling resolves the aforementioneddrawbacks of packet interval sampling. However, with both packetinterval sampling and flow interval sampling, the reporting is not ascomplete as monitoring and reporting on each and every flow.

SUMMARY

The invention sets forth various algorithms for sampling flows moreintelligently than random sampling based on flow or packet intervals.One embodiment employs a combination of random flow sampling and toptalker flow sampling. The reporting result is a fixed number of flowsfrom the random sampling (e.g., 10 random flows out of every 100 flows)and a variable number of flows depending on how many flows meet thepredetermined top talker criteria. A method of a network device in thisembodiment comprises receiving packets and determining the flows fromthe packets. Each of the flows is a stream of the packets sharing agroup of packet characteristics. Then the network device identifies asample of the flows and exports information on the sample of the flowsto an external collector for further analysis or processing. The sampleof the flows includes two parts. The first subset of the sample isdetermined by flow interval sampling and a second subset of the samplesrepresents top talkers determined by a predetermined criteria.Accordingly, the number of flows reported in the second subset dependson stringency of the predetermined criteria defining top talkers, whichare the flows that most impact traffic of the network device. Reportingon the top talkers provides information on major flows that may bemissed when reporting on flows only based on flow interval sampling.

The network device that implements this embodiment contains a forwardingplane and a control plane. The forwarding plane includes a packetreceiving module to receive packets and determine the flows from thepackets, a flow sampling module to identify a first subset of the flowsreceived from the packet receiving module based on flow intervalsampling and to report information on the flows in the first subset tothe interval-based flow exporter upon the flows expiration, and a flowanalysis module to analyze each of the flows received from the packetreceiving module for major characteristics defined by a predeterminedcriteria to identify a second subset of the flows as top talkers and toreport information on the flows in the second subset to the top talkerflow exporter upon the flows' expiration. The control plane includes aninterval-based flow exporter to export the information on the flows inthe first subset from the flow sampling module to an external collectorand a top talker flow exporter to export the information on the flows inthe second subset from the flow analysis module to the externalcollector.

Another embodiment employs flow sampling based on bandwidth utilization.An initial number N of flows is determined as the sample per timeinterval and evaluated on whether its bandwidth utilization exceeds athreshold value, e.g., 70% of total bandwidth captured by N flows. Ifthese N flows do not capture more than 70% of the total bandwidth, thentwo things are done. (a) a small percentage, for example 10% of these Nflows, which are the lowest bandwidth contributors based on the life ofthe flow are pruned, and (b) N is increased for the next time interval.If the bandwidth of these N flows exceeds the threshold, then N ismaintained for the next time interval. The reporting result is N flowsthat aim to capture most of the bandwidth. A method of a network devicein this embodiment includes receiving packets at a forwarding plane ofthe network device during a sampling time interval, creating a flowdescriptor for each of the flows, and including flow information in onlya subset of the flow descriptors. Values are obtained by measuring totalbandwidth consumed by the flows represented by all the flow descriptorsduring the sampling time interval and total bandwidth consumed by theflows represented by the subset of the flow descriptors during thesampling time interval. Dividing the total bandwidth of the flowsrepresented by all the flow descriptors during the sampling timeinterval by the total bandwidth of the flows represented by the subsetof the flow descriptors during the sampling time interval uponexpiration of the sampling time interval results in a bandwidthutilization value and it is determined whether the bandwidth utilizationexceeds a threshold value. If so, the network element maintains a numberof flow descriptors in the subset of the flow descriptors taken in thesampling time interval for a next sampling time interval. If not, thenetwork element increases the number of flow descriptors in the subsetof the flow descriptors taken in the sampling time interval for the nextsampling time interval, aiming to achieve a bandwidth utilization thatexceeds the threshold value in the next sampling time interval. Flowsthat expire are reported from the forwarding plane to a control plane ofthe network device, and then exported to an external collector forfurther analysis or processing. The flow information reported to thecontrol plane represents a sample of flows that most impact traffic ofthe network device in terms of bandwidth size.

The network device of the preceding embodiment contains differentmodules on the forwarding plane and the control plane. The forwardingplane includes a flow descriptor creation module to receive packets at aforwarding plane during a sampling time interval and create a flowdescriptor for each of the flows, a total bandwidth tracking module tomeasure total bandwidth consumed by the flows represented by all theflow descriptors created by the flow descriptor creation module duringthe sampling time interval, and a sampled bandwidth tracking module tomeasure total bandwidth consumed by the flows represented by the subsetof the flow descriptors created by the flow descriptor creation moduleduring the sampling time interval. To calculate bandwidth utilization,the forwarding plane includes a bandwidth calculation module to dividethe total bandwidth of the flows represented by all the flow descriptorsmeasured by the total bandwidth tracking module by the total bandwidthof the flows represented by the subset of the flow descriptors measuredby the sampled bandwidth tracking module upon expiration of the samplingtime interval to obtain a bandwidth utilization and determine whetherthe bandwidth utilization exceeds a threshold value. A flow descriptorcreation adjustment module maintains a number of flows in the subset ofthe flows taken in the sampling time interval for a next sampling timeinterval when the bandwidth utilization exceeds the threshold value andincreases the number of flows in the subset of the flows taken in thesampling time interval for the next sampling time interval when thebandwidth utilization does not exceed the threshold value. A flowreporting module reports the flow information represented by the flowdescriptors in the subset upon the flows' expiration from the forwardingplane to a control plane. In the control plane, a flow exporter exportsthe flow information reported to the control plane from the controlplane to an external collector.

A further embodiment employs flow sampling based on buckets organized bya top talker criterion. The capacity of all of the buckets combined iscapped at a value of M number of flows. If the capacity M has beenreached, this embodiment drops one low talker flow to accommodate a newflow. Flows are reported when they expire based on active or inactivetimeout and if they meet predetermined top-talking criteria, such asminimum number of packets or bytes. Not all M flows need be reported.The reporting result is a number of flows up to M. If the total numberof flows exceeds M, then up to M top talker flows are reported. A methodof this embodiment includes receiving a packet at a forwarding plane ofthe network device, determining whether the packet is part of anexisting flow already tracked in one of the plurality of buckets rangingfrom a least-significant bucket to a most-significant bucket in terms ofa predetermined criteria that identifies top talkers. Each of theplurality of buckets sort the flows tracked therein by order of leastrecently used at a tail of each bucket and most recently used at a headof each bucket. Upon determination that the packet is part of theexisting flow already tracked in one of the plurality of buckets, thenetwork device adds the packet to that existing flow and moves thatexisting flow to the head of a bucket of the plurality of buckets. Thebucket for that existing flow is selected based on the predeterminedcriteria. Upon determination that the packet is not part of any existingflows already tracked in one of the plurality of buckets, the networkdevice determines whether a total number of flows tracked in theplurality of buckets of the forwarding plane has reached a maximum limitand discards a flow from the tail of the least-significant bucket onlywhen the total number of flows in the plurality of buckets of theforwarding plane has reached a maximum limit. The flow is discarded toallow a new flow to be created without causing the total number of flowsto exceed the maximum limit and because the flow to be discarded is theleast recently used flow in the least-significant bucket. The networkdevice can then create a new flow for the packet at the head of theleast-significant bucket. Information is reported on the flows trackedin the plurality of buckets upon the flows' expiration from theforwarding plane to a control plane of the network device andsubsequently exported to an external collector for further analysis orprocessing by the external collector. Reporting only the information onthose flows that remain tracked in any of the plurality of buckets bynot being discarded upon the flows' expiration ensures that informationon the top talkers is reported and also guarantees that information onat least one flow is reported because all flows created by the networkdevice are reported up to the maximum limit.

A network device directed to this embodiment contains the followingmodules. A forwarding plane of the network device includes a packetreceiving module to receive a packet and a flow organizing module havingthe plurality of buckets. The flow organizing module determines whetherthe packet is part of an existing flow already tracked in one of theplurality of buckets ranging from a least-significant bucket to amost-significant bucket in terms of a predetermined criteria thatidentifies top talkers. This module moves, discards, and adds flows tobuckets in accordance with the above method. A flow reporting modulereports information on the flows tracked in the plurality of bucketsupon the flows' expiration from the forwarding plane to a control plane.The control plane includes a flow exporter to export the information onthe flows reported to the control plane from the control plane to anexternal collector for further analysis or processing by the externalcollector.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 illustrates an exemplary system for network flow samplingaccording to one embodiment of the invention;

FIG. 2 illustrates an exemplary network device according to oneembodiment of the invention;

FIG. 3 is a data flow diagram of a network device according to oneembodiment of the invention;

FIG. 4 illustrates an exemplary network device according to oneembodiment of the invention;

FIG. 5 is a data flow diagram of a network device according to oneembodiment of the invention;

FIG. 6 illustrates an exemplary network device according to oneembodiment of the invention;

FIG. 7 illustrates an exemplary module in the network device of FIG. 6according to one embodiment of the invention;

FIG. 8 illustrates an exemplary module in the network device of FIG. 6according to one embodiment of the invention; and

FIG. 9 is a data flow diagram of a network device according to oneembodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description. Those ofordinary skill in the art, with the included descriptions, will be ableto implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other.

The techniques shown in the figures can be implemented using code anddata stored and executed on one or more electronic devices (e.g., an endstation, a network element, etc.). Such electronic devices store andcommunicate (internally and/or with other electronic devices over anetwork) code and data using machine-readable media, such asmachine-readable storage media (e.g., magnetic disks; optical disks;random access memory; read only memory; flash memory devices;phase-change memory) and machine-readable communication media (e.g.,electrical, optical, acoustical or other form of propagated signals—suchas carrier waves, infrared signals, digital signals, etc.). In addition,such electronic devices typically include a set of one or moreprocessors coupled to one or more other components, such as one or morestorage devices, user input/output devices (e.g., a keyboard, atouchscreen, and/or a display), and network connections. The coupling ofthe set of processors and other components is typically through one ormore busses and bridges (also termed as bus controllers). The storagedevice and signals carrying the network traffic respectively representone or more machine-readable storage media and machine-readablecommunication media. Thus, the storage device of a given electronicdevice typically stores code and/or data for execution on the set of oneor more processors of that electronic device. Of course, one or moreparts of an embodiment of the invention may be implemented usingdifferent combinations of software, firmware, and/or hardware.

As used herein, a network device or element (e.g., a router, switch,bridge, etc.) is a piece of networking equipment, including hardware andsoftware, that communicatively interconnects other equipment on thenetwork (e.g., other network elements, end stations, etc.). Some networkelements are “multiple services network elements” that provide supportfor multiple networking functions (e.g., routing, bridging, switching,Layer 2 aggregation, session border control, Quality of Service, and/orsubscriber management), and/or provide support for multiple applicationservices (e.g., data, voice, and video). Subscriber end stations (e.g.,servers, workstations, laptops, palm tops, mobile phones, smartphones,multimedia phones, Voice Over Internet Protocol (VOID) phones, portablemedia players, GPS units, gaming systems, set-top boxes, etc.) accesscontent/services provided over the Internet and/or content/servicesprovided on virtual private networks (VPNs) overlaid on the Internet.The content and/or services are typically provided by one or more endstations (e.g., server end stations) belonging to a service or contentprovider or end stations participating in a peer to peer service, andmay include public webpages (free content, store fronts, searchservices, etc.). private webpages (e.g., username/password accessedwebpages providing email services, etc.), corporate networks over VPNs,etc. Typically, subscriber end stations are coupled (e.g., throughcustomer premise equipment coupled to an access network (wired orwirelessly)) to edge network elements, which are coupled (e.g. throughone or more core network elements) to other edge network elements, whichare coupled to other end stations (e.g., server end stations).

Some network elements include functionality for AAA (authentication,authorization, and accounting) protocols (e.g. RADIUS (RemoteAuthentication Dial-In User Service), Diameter, and/or TACAS+ (TerminalAccess Controller Access Control System). AAA can be provided through aclient/server model, where the AAA client is implemented on a networkelement and the AAA server can be implemented either locally on thenetwork element or on a remote end station (e.g., server end station)coupled with the network element. Authentication is the process ofidentifying and verifying a subscriber. For instance, a subscriber mightbe identified by a combination of a username and a password or through aunique key. Authorization determines what a subscriber can do afterbeing authenticated, such as gaining access to certain end stationinformation resources (e.g., through the use of access controlpolicies). Accounting is recording user activity. By way of a summaryexample, subscriber end stations may be coupled (e.g., through an accessnetwork) through an edge network element (supporting AAA processing)coupled to core network elements coupled to server end stations ofservice/content providers. AAA processing is performed to identify thesubscriber record for a subscriber. A subscriber record includes a setof attributes (e.g., subscriber name, password, authenticationinformation, access control information, rate-limiting information,policing information, etc.) used during processing of that subscriber'straffic.

Certain network elements (e.g., certain edge network elements)internally represent subscriber end stations (or sometimes customerpremise equipment (CPE) such as a residents gateway (e.g., a router,modem)) using subscriber circuits. A subscriber circuit uniquelyidentifies within the network element a subscriber session and typicallyexists for the lifetime of the session. Thus, a network elementtypically allocates a subscriber circuit when the subscriber connects tothat network element, and correspondingly de-allocates that subscribercircuit when that subscriber disconnects. Each subscriber sessionrepresents a distinguishable flow of packets communicated between thenetwork element and a subscriber end station (or sometimes CPE such as aresidential gateway or modem) using a protocol, such as thepoint-to-point protocol over another protocol (PPPoX) (e.g., where X isEthernet or Asynchronous Transfer Mode (ATM)), Ethernet, 802.1Q VirtualLAN (VLAN), Internet Protocol, ATM, etc. A subscriber session can beinitiated using a variety of mechanisms: manual provisioning a dynamichost configuration protocol (DHCP), DHCP/client-less internet protocolservice (CLIPS), Media Access Control (MAC) address tracking, etc. Forexample, the point-to-point protocol (PPP) is commonly used for DSLservices and requires installation of a PPP client that enables thesubscriber to enter a username and a password, which in turn may be usedto select a subscriber record. When DHCP is used (e.g., for cable modemservices), a username typically is not provided; but in such situationsthe MAC address of the hardware in the subscriber end station (or CPE)is provided. The use of DHCP and CLIPS on the network element capturesthe MAC addresses and uses these addresses to distinguish subscribersand access their subscriber records.

Certain network elements (e.g., certain edge network elements) use ahierarchy of circuits. The leaf nodes of the hierarchy of circuits aresubscriber circuits. The subscriber circuits have parent circuits in thehierarchy that typically represent aggregations of multiple subscribercircuits, and thus the network segments and elements used to provideaccess network connectivity of those end stations to the networkelement. These parent circuits may represent physical or logicalaggregations of subscriber circuits (e.g., a virtual local area network(VLAN), a private virtual circuit (PVC) (e.g., for Asynchronous TransferMode (ATM)), a circuit-group, a channel, a pseudo-wire, a physical portof the network element, and a link aggregation group). A circuit-groupis a virtual construct that allows various sets of circuits to begrouped together for configuration purposes, for example aggregate ratecontrol. A pseudo-wire is an emulation of a layer 2 point-to-pointconnection-oriented service. A link aggregation group is a virtualconstruct that merges multiple physical ports for purposes of bandwidthaggregation and redundancy. Thus, the parent circuits physically orlogically encapsulate the subscriber circuits.

Network elements are commonly separated into a control plane and a dataplane (sometimes referred to as a forwarding plane or a media plane). Inthe case that the network element is a router (or is implementingrouting functionality), the control plane typically determines how data(e.g., packets) is to be routed (e.g., the next hop for the data and theoutgoing port for that data), and the data plane is in charge offorwarding that data. For example, the control plane typically includesone or more routing protocols (e.g., Border Gateway Protocol (BGP),Interior Gateway Protocol(s) (IGP) (e.g., Open Shortest Path First(OSPF), Routing Information Protocol (RIP), Intermediate System toIntermediate System (IS-IS), etc.), Label Distribution Protocol (LDP),Resource Reservation Protocol (RSVP), etc.) that communicate with othernetwork elements to exchange routes and select those routes based on oneor more routing metrics.

Routes and adjacencies are stored in one or more routing structures(e.g., Routing Information Base (RIB), Label Information Base (LIB), oneor more adjacency structures, etc.) on the control plane. The controlplane programs the data plane with information (e.g., adjacency androute information) based on the routing structure(s). For example, thecontrol plane programs the adjacency and route information into one ormore forwarding structures (e.g., Forwarding Information Base (FIB),Label Forwarding Information Base (LFIB), and one or more adjacencystructures) on the data plane. The data plane uses these forwarding andadjacency structures when forwarding traffic.

Each of the routing protocols downloads route entries to a main RIBbased on certain route metrics (the metrics can be different fordifferent routing protocols). Each of the routing protocols can storethe route entries, including the route entries which are not downloadedto the main RIB, in a local RIB (e.g., an OSPF local RIB). A RIB modulethat manages the main RIB selects routes from the routes downloaded bythe routing protocols (based on a set of metrics) and downloads thoseselected routes (sometimes referred to as active route entries) to thedata plane. The RIB module can also cause routes to be redistributedbetween routing protocols.

For layer 2 forwarding, the network element can store one or morebridging tables that are used to forward data based on the layer 2information in this data.

Typically, a network element includes a set of one or more line cards, aset of one or more control cards, and optionally a set of one or moreservice cards (sometimes referred to as resource cards). These cards arecoupled together through one or more mechanisms (e.g., a first full meshcoupling the line cards and a second full mesh coupling all of thecards). The set of line cards make up the data plane, while the set ofcontrol cards provide the control plane and exchange packets withexternal network element through the line cards. The set of servicecards can provide specialized processing (e.g., Layer 4 to Layer 7services (e.g., firewall, IPsec, IDS, P2P), VoIP Session BorderController, Mobile Wireless Gateways (GGSN, Evolved Packet System (EPS)Gateway), etc.). By way of example, a service card may be used toterminate IPsec tunnels and execute the attendant authentication andencryption algorithms.

FIG. 1 illustrates an exemplary system for network flow samplingaccording to one embodiment of the invention. A different type of flowmonitoring can be implemented at each of the network devices accordingto resource capabilities and need. Three exemplary embodiments aredescribed herein. In FIG. 1, NetFlow Reporting element 140 serves as anexternal collector that receives flow information reported by each ofthe other network devices. The flows can be of different types.

Data center 105 reports application flows to NetFlow Reporting element140. Campus element 110 reports multicast flows and security flows toNetFlow Reporting element 140. Branch 120 and teleworker 130 report IPflows through a wireless access network to NetFlow Reporting element140. Along with the reporting on the flows, the network devices may alsoreport on the particular parameters used to determine which flows arereported. For example, if a network device reports on flows that containmore than 1 million packets, this network device would report on theseflows to NetFlow Reporting element 140 and additionally indicate toNetFlow Reporting element 140 that the flows being reported on are thosethat contain more than 1 million packets. NetFlow Reporting element 140can then use the flow information for usage-based accounting, trafficprofiling, traffic engineering, attack or intrusion detection, and QoSmonitoring as needed.

FIG. 2 illustrates an exemplary network device according to oneembodiment of the invention. This embodiment samples flows in two ways.One, by sampling based on flow intervals and two, by identifying the toptalkers. The reporting result to collector 140 is a fixed number offlows from the random sampling (e.g., 10 random flows out of every 100flows) and a variable number of flows depending on how many flows meetthe predetermined top talker criterion. These records are reported onseparate collector streams.

Network device 210 includes modules on forwarding plane 215 and controlplane 220. Forwarding plane 215 includes packet receiving module 225,flow sampling module 230, and flow analysis module 235. Packet receivingmodule 225 receives packets and determines flows from the packets. Flowsare defined as a unidirectional stream of packets that share a group ofpacket characteristics, such as Source IP address, destination IPaddress, source port for UDP or TCP, 0 for other protocols, destinationport for UDP or TCP, type and code for ICMP, or 0 for other protocols,IP protocol, ingress interface (SNMP ifIndex), and IP Type of Service.Flow sampling module 230 and flow analysis module 235 identifyrespective samples from the flows. Flow sampling module 230 identifies afirst subset of the flows based on random flow interval sampling. Flowanalysis module 235 identifies a second subset of flows by analyzingevery one of the flows to determine whether they are top talkers orheavy hitters. A predetermined criterion defines what a top talker orheavy hitter is. For example, one or more conditions are set that definetop talkers with respect to a total number of packets in the flow, atotal number of bytes in the flow, a number of packets per second in theflow, a number of bytes per second in the flow, and a lifetime of theflow.

Upon a flow's expiration, it is reported to control plane 220 if it wasidentified as a sample by flow sampling module 230 and/or a top talkerby flow analysis module 235. Flow sampling module 230 reports theinformation of the first subset to interval-based flow exporter 240 andflow analysis module 235 reports the information of the second subset totop-talker flow exporter 245. These two exporters export the respectiveinformation to external collector 140 through separate collectorstreams. If a particular flow is a top talker and also happened to beidentified as one of the flows to be sampled, information of this flowwould be reported to collector 140 through both collector streams.Furthermore, these two exporters 240, 245 also report the criterion usedto identify their respective subsets to collector 140. This way, thecollector knows what conditions were used to select the reported flows.

FIG. 3 is a data flow diagram of a network device according to oneembodiment of the invention. The operations of FIG. 3 will be describedwith reference to the exemplary embodiment of FIG. 2. However, it shouldbe understood that the operations of flow diagrams can be performed byembodiments of the invention other than those discussed with referenceto FIG. 2, and the embodiments discussed with reference to FIG. 2 canperform operations different than those discussed with reference to theflow diagrams.

Beginning at 310, network device 210 receives packets at packetreceiving module 225 of forwarding plane 215. Packet receiving module225 determines flows from the received packets at operation 315. Flowsampling module 230 analyzes these flows to identify a first subset ofthe flows based on a flow sampling interval at operation 320. Forexample, an interval may be 1 flow out of every 100 flows. Flow analysismodule 235 also analyzes these flows to identify a second subset of theflows according to a predetermined criterion at operation 325. Thepredetermined criterion includes one or more conditions that define aflow as a top talker or heavy hitter. At operation 330, a determinationis made whether any of the flows has expired. If the expired flow is oneof the flows identified by flow sampling module 230 in the first subsetor flow analysis module 235 in the second subset, then the respectivemodule reports information on the expired flow to control plane 220(operation 335). Flow sampling module 230 reports to interval-based flowexporter 240 and flow analysis module 235 reports to top-talker flowexporter 245. These exporters export the information on separatecollector channels to external collector 140, along with informationthat indicates how the reported flows were selected (operation 340). Inthis embodiment, regular flow based sampling is combined with top talkeranalysis so that flows that most impact traffic are sure to be reported.

FIG. 4 illustrates an exemplary network device according to oneembodiment of the invention. In this embodiment, network device 410samples flows based on bandwidth analysis. The reporting result is Nflows that aim to capture most of the bandwidth. Various modules worktogether to measure and calculate bandwidth utilization so that flowsampling measures can be adjusted accordingly.

In forwarding plane 415, flow descriptor creation module 425 receivespackets during a sampling time interval and creates a flow descriptorfor each of the flows. Two elements of bandwidth tracking are directedto the flows. Total bandwidth tracking module 430 measures the totalbandwidth consumed by the flows represented by all the flow descriptorsduring the sampling time interval, such as one second. Sampled bandwidthtracking module 440 measures the total bandwidth consumed by aninitialized subset of flows. This subset of flows can be, for example,100 randomly selected flows. The measurements taken by both thesetracking modules is provided to bandwidth calculation module 435, whichdetermines bandwidth utilization by the subset in terms of a percentagevalue. This is calculated by dividing the bandwidth of the subset offlows by the total bandwidth consumed by all the flows. The result iscompared to a predetermined threshold value. This threshold value is agoal in terms of bandwidth percentage that should be captured by thesubset. For example, a threshold value may be to have a subset of flowsthat captures 70% of the bandwidth of all flows. If the calculatedresult of bandwidth calculation module 435 achieves this goal, then flowdescriptor creation adjustment module 445 maintains that initializedvalue of number of flows in the subset for the next sampling timeinterval, e.g., the next second. If the goal is not met, then flowdescriptor creation adjustment module 445 increases the number of flowsconsidered as the subset for the next sampling time interval. Forexample, if 100 flows were initially taken as the subset, but onlyconsume 50% of the bandwidth, the next time interval may take 150 flowsin an attempt to see if 150 flows would capture at least 70% of thebandwidth.

Flow reporting module 450 reports flow information of expired flows toflow exporter 455 of control plane 420. Flow exporter 455 exports theflow information to external collector 140. It is noted that even if thebandwidth goal is not met, an expired flow in the subset would still bereported out. In addition, a maximum value may be preset to limit thenumber of total flow descriptors that flow descriptor creation module425 is permitted to create. For example, the number of flow descriptorsmay be limited to 1 million flows. If this maximum number of flows ismet, then flow descriptor creation module 425 is not permitted to createanother flow descriptor. However, if a new packet arrives and a new flowdescriptor needs to be created, flow descriptor creation module 425 canthen identify one of the flow descriptors in the subset of leastbandwidth. After this flow descriptor is discarded, a new flowdescriptor can be created for the incoming packet without the totalnumber of flow descriptors exceeding the 1 million maximum. Thisconfiguration accepts new packets that could potentially be a part offlows that consume a great amount of bandwidth when the total limit offlow descriptors has been met.

FIG. 5 is a data flow diagram of a network device according to oneembodiment of the invention. The operations of FIG. 5 will be describedwith reference to the exemplary embodiment of FIG. 4. However, it shouldbe understood that the operations of flow diagrams can be performed byembodiments of the invention other than those discussed with referenceto FIG. 4, and the embodiments discussed with reference to FIG. 1 canperform operations different than those discussed with reference to theflow diagrams.

Starting with operation 505, a sampling time interval such as one secondbegins. At 510, network device 410 receives packets at forwarding plane415. At 515, flow descriptor creation module 425 creates flowdescriptors for every flow but includes flow information (to be reportedlater) only for a subset “N” of flows. At operation 520, network device410 measures total bandwidth consumed by all flows and at operation 525,network device 410 measures total bandwidth consumed by N flows. If thesampling time interval of for example one second has expired, the methodproceeds to operation 535 where network device 410 calculates bandwidthutilization of the N flows out of the total number of flows. If thisbandwidth utilization value exceeds a predetermined threshold value(operation 540), then the value of N will be maintained for the nextsampling time interval, such as for the next second (operation 550). Ifthe threshold value is not met, then N will be increased to a highervalue for the next sampling time interval (operation 545). In oneembodiment, low bandwidth flows are pruned so as to make room forpotentially high bandwidth flows in the next interval.

At operation 555, network device 410 determines whether any of the Nflows have expired. If so, then information on these expired flows isreported by flow reporting module 450 to control plane 420 (operation560). This information is then exported to external collector 140(operation 565). In addition, flows can be reported even if they do notexpire according to other conditions. For instance, a time limit can beset for the flows such that if the flows exceed this time limit, thenthey will be reported even though they have not expired. This may bereferred to as active timeout to insure that these long flows arereported. Furthermore, inactive timeout refers to flows that have notreceived a new packet in a set amount of time and therefore are “agedout” and reported.

FIG. 6 illustrates an exemplary network device according to oneembodiment of the invention. This embodiment employs flow sampling basedon buckets organized by a top talker criterion. The capacity of all ofthe buckets combined is capped at a value of “M” number of flows. If thecapacity M has been reached, this embodiment drops one low talker flowto accommodate a new flow. The reporting result is a number of flows upto M. If the total number of flows is fewer than M, then all flows maybe reported. In one embodiment, all flows are reported when the numberof flows is fewer than M. In another embodiment, all flows do not needto be reported even though the number of flows is fewer than M. Instead,flows are reported based on given criterion, such as a top talkercriterion of minimum number of packets in the flow. Similarly, if thetotal number of flows exceeds M, then up to M top talker flows arereported. In one embodiment, M flows are reported when the number offlows exceeds M. In another embodiment, only those flows that meet apredetermined criterion are reported, such as a minimum number of bytesin the flow. For these criteria, a variety of top talker definitions canbe used. Network device 610 in this embodiment utilizes various modulesto organize the flows into these virtual buckets.

Forwarding plane 615 includes packet receiving module 625 to receivepackets and send them to flow organizing module 630. Flow organizingmodule 630 includes a plurality of buckets to organize the packets. Thismodule determines whether a received new packet is part of an existingflow already tracked in one of the plurality of buckets. If so, thenmodule 630 adds that new packet to the existing flow already tracked inone of the buckets. If the new packet is not part of an existing flowalready tracked in a bucket, then module 630 first determines whetherthe total number of flows tracked in these buckets has reached a maximumlimit. If the maximum limit has not been met, then a new flow is createdin a bucket. If the maximum limit has been met, then module 630 needs todiscard one of the flows to allow a new flow to be created. Module 630selects an insignificant flow to be discarded so that top talkers remaintracked. Details of flow organizing module 630 are described withreference to subsequent FIGS. 7 and 8.

Flow reporting module 635 reports the information of the flows trackedin the plurality of buckets upon their expiration. If a flow wasdiscarded by flow organizing module 630, it is no longer tracked by thebuckets and therefore would not be reported when it expires. Thisembodiment of tracking through top talker buckets ensures thatinformation on the top talkers is reported up to the maximum limit offlows permitted to be tracked. In the event that fewer than the maximumnumber of flows is tracked, then all flows would be reported. Flowexporter 640 of control plane 620 exports the information on thereported flows to external collector 140.

FIG. 7 illustrates an exemplary module in the network device of FIG. 6according to one embodiment of the invention. FIG. 7 depicts a detailedview of flow organizing module 630 and the buckets contained therein byway of specific example. Here, flow organizing module 630 includes 4buckets 710, 720, 730, 740. It is noted that the number of buckets maybe fewer or more depending on resources and preferences of a particularnetwork device.

As illustrated, the head of the buckets is at the top and the tail is atthe bottom. In each of the buckets, the most recently used flow is atthe head and the least recently used flow is at the tail of each bucket.In this example, the bucket 1 710 contains flows of packets from 0-100,bucket 2 720 contains flows of packets from 101-1000, bucket 3 730contains flows of packets from 1001-5000, and bucket 4 740 containsflows of packets more than 5000 in number. Accordingly, these bucketsconsider number of packets to be the condition by which top talker flowsare defined. As discussed earlier, top talkers can be defined by otheraspects instead.

In one example, packets are received for flows in order of F1, F2, F3,F4, and F5. Since F5 was most recently used, it is at the head of bucket1. Since F1 was least recently used, it is at the tail of bucket 1. Inthe event that a flow is to be discarded, F1 would be discarded becauseit is the least recently used flow of the least-significant bucket.Flows with a number of packets up to 100 are tracked in bucket 1 710. Itis noted that flow F3 includes 150 packets and therefore is tracked inbucket 2 720 is further noted that flow F3 must have began in bucket 1710 because all new flows are created with just one packet. As packetsare added to the existing tracked flows, they move up to other buckets.If a new flow is subsequently inserted into bucket 2 710, would go inthrough the head of the bucket and in this illustration would bepositioned above F3. Bucket 3 730 for flows containing 1001-5000 packetsand bucket 4 740 for flows containing more than 5000 packets are emptyat the moment because no flows contain that many packets yet. The nextfigure will illustrate the flow positions when new packets are receivedby network device 610 in an example.

FIG. 8 illustrates an exemplary module in the network device of FIG. 6according to one embodiment of the invention. FIG. 8 depicts a detailedview of flow organizing module 630 and the buckets contained therein byway of specific example. FIG. 8 is the end result of flows in bucketsafter the progression from FIG. 7 when new packets are received in thefollowing order: F3 receives 100 packets, then F4 receives 200 packets,then F2 receives 2000 packets, then F1 receives 200 packets, then 35packets for new flow F6 are received, and 80 packets for new flow F7 arereceived. FIG. 8 is best understood when viewed with FIG. 7.

The first event is flow F3 receives 100 packets. As shown in FIG. 7, F3used to contain 150 packets. FIG. 8 shows F3 containing 100+150=250packets and since F3 is still the only flow in bucket 2 720, it remainsin the same position. The second event is flow F4 receives 200 packets.F4 used to contain 10 packets according to FIG. 7 and now contains 210packets. F4 now contains too many packets to qualify under bucket 1 710.Bucket 2 720 is for flows with 101-1000 packets and F4, which contains210 packets, is moved out of bucket 1 710 and inserted at the head ofbucket 2 720, which is just above F3. The next event is F2 receives 2000packets. F2 used to contain 20 packets. As new packets were added, F2was bumped up to the head of bucket 2 720 as well. Then, when F2exceeded 1000 packets, it was bumped out of bucket 2 720 and into bucket3 730 which is for flows containing 1001-5000 packets. F2 is now theonly flow in bucket 3 730. The next event is F1 receives 200 packets. F1used to have 25 packets and now has 225 packets. Therefore, it fits inbucket 2 720 and is inserted at the head of bucket 2, right above F4.

Now, new packets are received for flows that do not yet exist in any ofthe buckets. First, 35 packets for new flow F6 are received. A flow forF6 is created upon the first new packet, and the remaining 34 packetsare added to that flow. F6 contains 35 packets and sits at the head ofbucket 1, right above F5. Then, 80 packets for new flow F7 are received.Analogous to F6, new flow F7 is created and resides at the head ofbucket 1710 because it contains 80 packets. In the example of FIG. 8,the maximum number of flows permitted to be tracked by buckets is morethan 7. For this reason, no flows needed to be discarded when the firstpacket for new F6 and the first packet for new F7 were received.

If the maximum number of flows permitted to be tracked was 7, a newpacket for flow that is not F1-F7 would be handled differently. Before anew flow for this packet can be created, an existing flow must first bediscarded. The flow to be discarded is the flow that lies at the tail ofthe least significant bucket, bucket 1 710. Continuing with thisexample, F5 would be discarded to allow for new F8 to be created. Bucket4 740 remains empty because no flows have more than 5000 packets. Whenany of the flows in any of the buckets expire, those are the flows thatare reported to control plane 620, and then to collector 140.

FIG. 9 is a data flow diagram of a network device according to oneembodiment of the invention. The operations of FIG. 9 will be describedwith reference to the exemplary embodiment of FIGS. 6-8. However, itshould be understood that the operations of flow diagrams can beperformed by embodiments of the invention other than those discussedwith reference to FIGS. 6-8, and the embodiments discussed withreference to FIGS. 6-8 can perform operations different than thosediscussed with reference to the flow diagrams.

Beginning with operation 910, network device 610 receives packets atforwarding plane 615. Packet organizing module 630 checks to see if thepacket is on a flow already tracked in buckets (operation 915). If so,packet organizing module 630 adds this packet to the existing flow(operation 920). The flow that just increased in packet size is moved tothe head of the appropriate bucket according to the parameters thatdefine top talkers (operation 925). If the new packet is not on any ofthe flows tracked in the buckets, then another check is performed to seeif the number of total flows tracked in the buckets has reached amaximum limit (operation 930). If so, then the flow that lies at thetail of the least significant bucket is discarded to make room for a newflow (operation 935). If the maximum limit has not been reached, networkdevice 610 is permitted to create a new flow at the head of the leastsignificant bucket (operation 940). For now, this new flow contains justone packet. As new packets are received on this flow, it may move toanother bucket.

At operation 945, network device 610 determines whether any of the flowsin any of the buckets have expired. When flows expire, information onthese flows are reported to control plane 620 (operation 950) and thenexported to collector 140 (operation 955).

While the flow diagrams in the figures show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.).

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

1. A method in a network device for performing sampling-based monitoringof flows, the method comprising the steps of: receiving packets;determining the flows from the packets, wherein each of the flows is astream of the packets sharing a group of packet characteristics;identifying a sample of the flows; and exporting information on thesample of the flows to an external collector for further analysis orprocessing by the external collector, wherein the information includesat least one of source IP address, destination IP address, source portnumber, destination port number, number of packets in the flow, numberof bytes in the flow, time of first packet of the flow, or time of lastpacket of the flow, wherein the sample of the flows includes a firstsubset of the flows based on flow interval sampling and a second subsetof the flows representing top talkers based on a predetermined criteria,wherein a number of flows in the second subset depends on stringency ofthe predetermined criteria and the top talkers are flows that mostimpact traffic of the network device, whereby reporting on the toptalkers provides information on major flows that may be missed whenreporting on flows only based on flow interval sampling.
 2. The methodof claim 1, wherein identifying the sample of the flows comprises thesteps of: identifying the first subset of the flows based on flowinterval sampling; analyzing each of the flows for major characteristicsdefined by the predetermined criteria to identify the second subset ofthe flows as the top talkers; and permitting the information on theflows in the first subset and the second subset to be exported to theexternal collector upon the flows' expiration.
 3. The method of claim 2,wherein exporting the information on the sample of the flows comprisingthe steps of: exporting the information on the first subset through afirst collector stream to the external collector; and exporting theinformation on the second subset through a second collector stream tothe external collector.
 4. The method of claim 2, wherein thepredetermined criteria that defines the top talkers comprise at leastone of a total number of packets in the flow, a total number of bytes inthe flow, a number of packets per second in the flow, a number of bytesper second in the flow, or a lifetime of the flow.
 5. The method ofclaim 4, further comprising the step of: reporting the predeterminedcriteria to the external collector.
 6. A network device for performingsampling-based monitoring of flows, comprising: a forwarding planehaving memory and CPU including: a packet receiving module to receivepackets and determine the flows from the packets, wherein each of theflows is a stream of the packets received on the network device sharinga group of packet characteristics; a flow sampling module to identify afirst subset of the flows received from the packet receiving modulebased on flow interval sampling and to report information on the flowsin the first subset to the interval-based flow exporter upon the flows'expiration; and a flow analysis module to analyze each of the flowsreceived from the packet receiving module for major characteristicsdefined by a predetermined criteria to identify a second subset of theflows as top talkers and to report information on the flows in thesecond subset to the top talker flow exporter upon the flows'expiration, wherein the top talkers are the flows that most impacttraffic of the network device, and wherein the information includes atleast one of source IP address, destination IP address, source portnumber, destination port number, number of packets in the flow, numberof bytes in the flow, time of first packet of the flow, or time of lastpacket of the flow; and a control plane having memory and CPU including:the interval-based flow exporter to export the information on the flowsin the first subset from the flow sampling module to an externalcollector; and the top talker flow exporter to export the information onthe flows in the second subset from the flow analysis module to theexternal collector, whereby reporting on the top talkers providesinformation on major flows that may be missed when reporting on flowsonly based on flow interval sampling.
 7. The network device of claim 6,wherein the interval-based flow exporter to export the information onthe first subset through a first collector stream to the externalcollector and the top talker flow exporter to export the information onthe second subset through a second collector stream to the externalcollector.
 8. The network device of claim 6, wherein the predeterminedcriteria that defines the top talkers comprise at least one of a totalnumber of packets in the flow, a total number of bytes in the flow, anumber of packets per second in the flow, a number of bytes per secondin the flow, or a lifetime of the flow.
 9. The network device of claim8, wherein the top talker flow exporter to report the predeterminedcriteria to the external collector.
 10. A method in a network device forperforming sampling-based monitoring of flows in terms of bandwidth, themethod comprising the steps of: receiving packets at a forwarding planeof the network device during a sampling time interval; creating a flowdescriptor for each of the flows, wherein each of the flows is a streamof the packets sharing a group of packet characteristics; including flowinformation in only a subset of the flow descriptors, wherein the flowinformation includes at least one of source IP address, destination IPaddress, source port number, destination port number, number of packetsin the flow, number of bytes in the flow, time of first packet of theflow, or time of last packet of the flow; measuring total bandwidthconsumed by the flows represented by all the low descriptors during thesampling time interval; measuring total bandwidth consumed by the flowsrepresented by the subset of the flow descriptors during the samplingtime interval; dividing the total bandwidth of the flows represented byall the flow descriptors during the sampling time interval by the totalbandwidth of the flows represented by the subset of the flow descriptorsduring the sampling time interval upon expiration of the sampling timeinterval to obtain a bandwidth utilization; determining whether thebandwidth utilization exceeds a threshold value; upon determination thatthe bandwidth utilization exceeds the threshold value, maintaining anumber of flow descriptors in the subset of the flow descriptors takenin the sampling time interval for a next sampling time interval; upondetermination that the bandwidth utilization does not exceed thethreshold value, increasing the number of flow descriptors in the subsetof the flow descriptors taken in the sampling time interval for the nextsampling time interval, whereby increasing the number of flowdescriptors that represent the subset aims to result in the bandwidthutilization exceeding the threshold value in the next sampling timeinterval; reporting the flow information in the subset upon the flows'expiration from the forwarding plane to a control plane of the networkdevice; exporting the flow information reported to the control planefrom the control plane to an external collector, whereby the flowinformation reported to the control plane represents a sample of flowsthat most impact traffic of the network device in terms of bandwidthsize for further analysis or processing by the external collector. 11.The method of claim 10, further comprising the step of: reporting thethreshold value to the external collector.
 12. The method of claim 10,wherein a maximum value limits a number of flow descriptors that arepermitted to be created.
 13. The method of claim 12, further comprisingthe step of: discarding a flow descriptor in the subset of flowdescriptors of least bandwidth to permit a new flow descriptor to becreated without the number of flow descriptors exceeding the maximumvalue.
 14. A network device for performing sampling-based monitoring offlows in terms of bandwidth, comprising: a forwarding plane havingmemory and CPU including: a flow descriptor creation module to receivepackets at a forwarding plane during a sampling time interval and createa flow descriptor for each of the flows, wherein each of the flows is astream of the packets sharing a group of packet characteristics, whereinflow information is included in only a subset of the flow descriptors,and wherein the flow information includes at least one of source IPaddress, destination IP address, source port number, destination portnumber, number of packets in the flow, number of bytes in the flow, timeof first packet of the flow, or time of last packet of the flow; a totalbandwidth tracking module to measure total bandwidth consumed by theflows represented by all the flow descriptors created by the flowdescriptor creation module during the sampling time interval; a sampledbandwidth tracking module to measure total bandwidth consumed by theflows represented by the subset of the flow descriptors created by theflow descriptor creation module during the sampling time interval; abandwidth calculation module to divide the total bandwidth of the flowsrepresented by all the flow descriptors measured by the total bandwidthtracking module by the total bandwidth of the flows represented by thesubset of the flow descriptors measured by the sampled bandwidthtracking module upon expiration of the sampling time interval to obtaina bandwidth utilization and determine whether the bandwidth utilizationexceeds a threshold value; a flow descriptor creation adjustment moduleto maintain a number of flows in the subset of the flows taken in thesampling time interval for a next sampling time interval upondetermination by the bandwidth calculation module that the bandwidthutilization exceeds the threshold value and to increase the number offlows in the subset of the flows taken in the sampling time interval forthe next sampling time interval upon determination by the bandwidthcalculation module that the bandwidth utilization does not exceed thethreshold value; and a flow reporting module to report the flowinformation represented by the flow descriptors in the subset upon theflows' expiration from the forwarding plane to a control plane; and thecontrol plane having memory and CPU including: a flow exporter to exportthe flow information reported to the control plane from the controlplane to an external collector, whereby the flow information reported tothe control plane represents a sample of flows that most impact trafficof the network device in terms of bandwidth size for further analysis orprocessing by the external collector.
 15. The network device of claim14, wherein the flow exporter to report the threshold value to theexternal collector.
 16. The network device of claim 14, wherein amaximum value limits a number of descriptors that the flow descriptorcreation module is permitted to create.
 17. The network device of claim16, wherein the flow descriptor creation module to discard a flowdescriptor in the subset of flow descriptors of least bandwidth topermit a new flow descriptor to be created without the number of flowdescriptors exceeding the maximum value.
 18. A method in a networkdevice for performing sampling-based monitoring of flows in a pluralityof buckets, the method comprising the steps of: receiving a packet at aforwarding plane of the network device; determining whether the packetis part of an existing flow already tracked in one of the plurality ofbuckets ranging from a least-significant bucket to a most-significantbucket in terms of a predetermined criteria that identifies top talkers,wherein the top talkers are the flows that most impact traffic of thenetwork device, wherein each of the plurality of buckets sort the flowstracked therein by order of least recently used at a tail of each bucketand most recently used at a head of each bucket; upon determination thatthe packet is part of the existing flow already tracked in one of theplurality of buckets, performing the following steps: adding the packetto that existing flow; and moving that existing flow to the head of abucket of the plurality of buckets, the bucket for that existing flow isselected based on the predetermined criteria; upon determination thatthe packet is not part of any existing flows already tracked in one ofthe plurality of buckets, performing the following steps: determiningwhether a total number of flows tracked in the plurality of buckets ofthe forwarding plane has reached a maximum limit; discarding a flow fromthe tail of the least-significant bucket only when the total number offlows in the plurality of buckets of the forwarding plane has reached amaximum limit, whereby the flow is discarded to allow a new flow to becreated without causing the total number of flows to exceed the maximumlimit and because the flow to be discarded is the least recently usedflow in the least-significant bucket; and creating a new flow for thepacket at the head of the least significant bucket; reportinginformation on the flows tracked in the plurality of buckets upon theflows' expiration from the forwarding plane to a control plane of thenetwork device, wherein the information includes at least one of sourceIP address, destination IP address, source port number, destination portnumber, number of packets in the flow, number of bytes in the flow, timeof first packet of the flow, or time of last packet of the flow, wherebyreporting only the information on those flows that remain tracked in anyof the plurality of buckets by not being discarded upon the flows'expiration ensures that information on the top talkers is reported andalso guarantees that information on at least one flow is reportedbecause all flows created by the network device are reported up to themaximum limit; and exporting the information on the flows reported tothe control plane from the control plane to an external collector forfurther analysis or processing by the external collector.
 19. The methodof claim 18, wherein the predetermined criteria that identifies the toptalkers is based on at least one of a total number of packets in theflow, a total number of bytes in the flow, a number of packets persecond in the flow, a number of bytes per second in the flow, or alifetime of the flow.
 20. The method of claim 19, wherein each of theplurality of buckets is designated for flows containing a differentpredetermined range of packets.
 21. The method of claim 20, wherein theleast-significant bucket is designated to track flows containing alowest number of packets and the most-significant bucket is designatedto track flows containing a highest number of packets.
 22. A networkdevice for performing sampling-based monitoring of flows in a pluralityof buckets, comprising: a forwarding plane having memory and CPUincluding; a packet receiving module to receive a packet; a floworganizing module having the plurality of buckets, the flow organizingmodule to determine whether the packet is part of an existing flowalready tracked in one of the plurality of buckets ranging from aleast-significant bucket to a most-significant bucket in terms of apredetermined criteria that identifies top talkers, wherein the toptalkers are the flows that most impact traffic of the network device,wherein each of the plurality of buckets sort the flows tracked thereinby order of least recently used at a tail of each bucket and mostrecently used at a head of each bucket, wherein upon determination thatthe packet is part of the existing flow already tracked in one of theplurality of buckets, the flow organizing module to add the packet tothat existing flow and move that existing flow to the head of a bucketof the plurality of buckets, the bucket for that existing flow isselected based on the predetermined criteria, and wherein upondetermination that the packet is not part of any existing flows alreadytracked in one of the plurality of buckets, the flow organizing moduleto determine whether a total number of flows tracked in the plurality ofbuckets of the forwarding plane has reached a maximum limit, discard aflow from the tail of the least-significant bucket only when the totalnumber of flows in the plurality of buckets of the forwarding plane hasreached a maximum limit, whereby the flow is discarded to allow a newflow to be created without causing the total number of flows to exceedthe maximum limit and because the flow to be discarded is the leastrecently used flow in the least-significant bucket, and create anew flowfor the packet at the head of the least-significant bucket; and a flowreporting module to report information on the flows tracked in theplurality of buckets upon the flows' expiration from the forwardingplane to a control plane, wherein the information includes at least oneof source IP address, destination IP address, source port number,destination port number, number of packets in the flow, number of bytesin the flow, time of first packet of the flow, or time of last packet ofthe flow, whereby reporting only the information on those flows thatremain tracked in any of the plurality of buckets by not being discardedupon the flows' expiration ensures that information on the top talkersis reported and also guarantees that information on at least one flow isreported because all flows created by the network device are reported upto the maximum limit; and the control plane having memory and CPUincluding: a flow exporter to export the information on the flowsreported to the control plane from the control plane to an externalcollector for further analysis or processing by the external collector.23. The network device of claim 22, wherein the predetermined criteriathat identifies the top talkers is based on at least one of a totalnumber of packets in the flow, a total number of bytes in the flow, anumber of packets per second in the flow, a number of bytes per secondin the flow, or a lifetime of the flow.
 24. The network device of claim23, wherein each of the plurality of buckets is designated for flowscontaining a different predetermined range of packets.
 25. The networkdevice of claim 24, wherein the least-significant bucket is designatedto track flows containing a lowest number of packets and themost-significant bucket is designated to track flows containing ahighest number of packets.